As known by the industry, the main component of a typical solder alloy material is a Pb—Sn alloy. Lead is harmful to a human body and will cause an environmental contamination. Therefore, researches on a lead-free solder material are imperative. A Sn—Ag eutectic alloy has a tensile strength higher than that of a conventional Pb—Sn alloy, but has a high melting point of about 221° C., which is much higher than the melting point (183.5° C.) of a Pb—Sn eutectic alloy. Therefore, such an alloy will cause an increase in the cost of facility. Furthermore, a high temperature is liable to cause a breakdown on the electric elements. Many patents try to reduce the melting point of a Sn—Ag eutectic alloy by adding a small amount of other alloy components, e.g. Cu, Zn, Bi, In and Sb, into a tri-element, tetra-element or penta-element system mainly consisting of a Sn—Ag eutectic alloy. Some of their melting points are still higher than 200° C. Even though the addition of a large amount of Bi and In can reduce the melting point of the alloy, the cost of the alloy has been dramatically increased. For example: Sn—Ag—Cu, U.S. Pat. No. 5,527,628 (1996); Sn—Ag—Zn—Bi, U.S. Pat. No. 5,993,736 (1999); Sn—Ag—Bi—In, U.S. Pat. No. 5,958,333 (1999), U.S. Pat. No. 5,843,371 (1998), U.S. Pat. No. 5,658,528(1997); Sn—Ag—Bi—Cu—In, U.S. Pat. No. 5,918,795 (1999); Sn—Ag—In—Bi—Sb, U.S. Pat. No. 5,733,501 (1998); Sn—Ag—Zn—In—Bi, U.S. Pat. No. 5,762,866 (1998).